Results: a) Serosal application of 1, 10 and 100 micrograms/ml ethanol caused 8 percent, 20 percent, and 29 percent increase in active Na ion transport respectively (Table 1). The stimulation of Na ion transport with 10 and 100 microgram/ml ethanol was signifiantly different from the control readings (p less than 0.01). b) Serotonin 10 to the minus 9th power, 10 to the minus 8th power and 10 to the minus 7th power micrograms/ml produced 10 percent, 19 percent and 28 percent increase in Na ion transport respectively (p less than 0.01) (Table 1). c) Serotonin in concentrations of 10 to the minus 9th power to 10 to the minus 7th power microgram/ml and ethanol in concentrations of 1 to 100 microgram/ml together showed a positive synergistic interaction on active Na ion transport. d) Vasopressin alone stimulated Na ion transport by 120 to 140 percent, alcohol alone by 30 to 40 percent. When the two were combined, their effects were simply additive. There is good evidence to indicate that vasopressin increases the active Na ion transport, primarily by increasing the permeability of the mucosa to sodium. Since one of the possible sites of ethanol action on active ionic transport is to enhance the actual ATP/Phase pump, a comparison of actions of vasopressin on active Na ion transport, in the presence and absence of ethanol, was conducted in substrate enriched bladder. If ethanol enhances the transport system, one would expect potentiation of vasopressin response in presence of ethanol. Our finding suggests no direct action of ethanol on the Na ion pump. Our observations favor the hypothesis that ethanol exerts a direct effect on the mucosal barrier and increases Na ion permeability (be it actively or passively).